Enhanced Vitamin D₃ Adsorption Through Novel Hydrophobic Halloysite–Alginate Biopolymer Composites

This study presents a sustainable strategy to enhance polymer encapsulation, adsorption, and functional properties by chemically modifying sodium alginate with hydrophobic groups. Hydrophobic alginate derivatives were synthesized via a solvent-free method using hexadecyl trimethylammonium bromide, resulting in nanoparticles capable of effectively capturing non-polar compounds. To further improve compatibility within alginate-based biocomposites, halloysite nanotubes were modified through ball milling and surfactant-assisted treatments. The resulting nanocomposites (MBHA and MHHA) exhibited significantly enhanced adsorption and controlled release behavior, as confirmed by FTIR analysis of hexadecyl alginate ester conjugation. Vitamin D₃ adsorption followed the Langmuir isotherm, with high correlation coefficients (R² = 0.998 for MBHA and R² = 0.991 for MHHA), indicating monolayer adsorption on a homogenous surface. Kinetic modeling revealed that the adsorption process adhered to a pseudo-second-order model (R² = 0.9969 for MBHA and R² = 0.999 for MHHA), suggesting that chemisorption was the dominant rate-controlling mechanism. These results demonstrate the critical role of surface modification in designing nano-engineered biopolymers with superior adsorption, stability, and release profiles, offering sustainable applications in medicine, agriculture, and environmental remediation.